Microsoft is delaying its regular Patch Tuesday round of security fixes this month. The software giant is blaming a “last minute issue” for the delay, and now plans to release the patches on March 14th, a whole month after they were supposed to go live. Microsoft was expected to patch a zero-day flaw in the company’s file sharing protocol, SMB, with its February patches, but Windows machines will now be left vulnerable to in-the-wild attacks until March 14th.

The month delay is unprecedented, and it’s rare that Microsoft even delays individual patches let alone the entire Patch Tuesday release. Microsoft first moved to a regular monthly patch release schedule in October 2003, citing a reduction of cost for distributing patches and the ability for system admins to work on a regular schedule of testing and deployment.

Microsoft isn’t saying exactly why this month’s Patch Tuesday is delayed, only that the company discovered “a last minute issue that could impact some customers and was not resolved in time for our planned updates today.” ZDNet reports that Microsoft was having problems with its patch build system, but the company isn’t providing any additional information.